1. Field of the Invention
The present invention relates to an ink, and an ink cartridge and an ink jet recording process using such an ink.
2. Description of the Related Art
An image recorded with an ink containing a pigment involves a problem that its glossiness is low. In order to solve this problem, an ink further containing a water-soluble polyurethane polymer in addition to the pigment has been investigated (Japanese Patent Application Laid-Open No. 2006-070123, Patent Literature 1).
In addition, an ink containing an ethylene oxide-propylene oxide type surfactant (EO-PO type surfactant) has been investigated for improving the glossiness (Japanese Patent Application Laid-Open No. 2005-082663, Patent Literature 2). The ink containing the EO-PO type surfactant has also been investigated in Japanese Patent Application Laid-Open No. 2009-007556 (Patent Literature 3) and Japanese Patent Application Laid-Open No. 2010-018741 (Patent Literature 4). Patent Literature 2 describes that an ink containing an EO-PO type surfactant having a weight-average molecular weight less than 1,000 can improve the glossiness of an image. Patent Literature 3 describes that an ink containing an EO-PO type surfactant having specific acid value and weight-average molecular weight and a polymer can improve the scratch resistance of an image and the ejection stability of the ink at the same time. Patent Literature 4 describes that an EO-PO type surfactant having a weight-average molecular weight of 15,000 or more is caused to be contained as a stabilizer in an ink, thereby improving the storage stability and ejection stability of the ink.